The present invention relates to a reticle protection member, a reticle-carrying device, an exposure device, and a method for carrying a reticle, with specific advantageous applications to EUV exposure devices.
Following recent miniaturization of semiconductor integrated circuits, projection lithography technology using EUV light with a shorter wavelength (11-14 nm) instead of conventional ultraviolet radiation has been developed with the object of increasing the resolution of optical systems restricted by a light diffraction limit. This technology has recently been called EUV (Extreme UltraViolet) lithography and it is expected to provide a resolution of 70 nm or less that could not be realized with conventional optical lithography using light radiation with a wavelength of about 190 nm.
A complex index of refraction, n, of a substance in a wavelength region of the EUV light is represented by n=1−δ−ik (i is a complex symbol). The imaginary portion k of this index of refraction represents absorption by extreme ultraviolet radiation. Because δ and k are much smaller than 1, the index of refraction in this region is very close to 1. Therefore, an optical system using reflection can be employed without using the conventional optical elements of a transmission refraction type such as lenses.
FIG. 12 is a general view of such an EUV exposure device. EUV light 32 emitted from an EUV light source 31 enters an illumination optical system 33, becomes an almost parallel light flux after being reflected by a concave reflective mirror 34 acting as a collimator mirror, and enters an optical integrator 35 comprising a pair of fly-eye mirrors 35a and 35b. For example, fly-eye mirrors disclosed in U.S. Pat. No. 6,452,661 can be used as the pair of fly-eye mirrors 35a and 35b. The structure and operation of fly-eye mirrors is described in greater detail in U.S. Pat. No. 6,452,661 and the explanation thereof is omitted.
An essentially extended light source having the prescribed shape is formed in the vicinity of the reflective surface of the second fly-eye mirror 35b, that is, in the vicinity of the outgoing surface of the optical integrator 35. The light from the essentially extended light source is deflected by a plane reflective mirror 36 and then forms an illumination region in the form of a narrow long circular arc on a reticle R (an aperture plate for forming the illumination region in the form of a circular arc is not shown in the figure). Light from the pattern of the illuminated reticle R forms an image of the reticle pattern on a wafer W via a projection optical system PL comprising a plurality of reflective mirrors (six reflective mirrors Ml to M6 are shown as an example in FIG. 12). The reticle R is held on a reticle stage, the wafer W is held on a wafer stage, and the entire pattern image of the reticle R surface is transferred on the wafer W by moving (scanning) the reticle stage and wafer stage.